Automatic Implantable Cardioverter Defibrillator/Permanent Pacemaker Interaction: Loss of Pacemaker Capture Following AICD Discharge

A 78-year-old man treated with amiodarone for recurrent ventricular tachycardia, had sequential placement of a bipolar VVI pacemaker and an automatic implantable cardioverter defibrillator (AICD). During defibrillation threshold testing, there was failure to capture of the pacer in the post-shock period. The time of failure to capture appeared energy-related: the greater the energy delivered, the longer the failure to capture. Careful attention will be necessary in constructing combined AICD/pacemaker units.     

Hemodynamic Effect of Propafenone and the Experience in Patients with Congestive Heart Failure

The effects of propafenone on left ventricular function and hemodynamics are presented in this study. In one group of 13 patients who underwent electrophysiological testing and subsequent chronic oral therapy with propafenone, eight had left ventricular ejection fractions determined by nuclear study before and during therapy with the drug. Initial measurements ranged from 22% to 39% (mean 30%), while those on chronic therapy showed no statistical difference and ranged from 22% to 48% (mean 30%). In a separate dose titration study of 14 patients, left ventricular ejection fraction showed a modest but significant decrease (52%± 9% to 48%± 11%; p < 0.05). This change was more marked in patients with an initial low ejection fraction. Propafenone appears to be safe in these patients but should be administered with caution in patients with particularly low ejection fractions.     

INTRAVENOUS GLUCOSE TOLERANCE, PLASMA INSULIN, FREE FATTY ACIDS AND β-HYDROXYBUTYRATE IN UNDERWEIGHT NEWBORN INFANTS

Blood glucose, plasma insulin, FFA and β-hydroxybutyrate values during intravenous glucose tolerance were reported in 20 small for gestational age (SGA) and 15 appropriate for gestational age (AGA) low birthweight infants. The babies were divided into three groups according to their age when tested; <24 hours, 24–48 hours and >48 hours. Both the SGA and AGA infants cleared glucose more rapidly with increasing age. The change was more marked in the SGA babies. The clearance rates were similar to those reported in normal full-sized infants. The insulin values before the glucose load were similar in all groups and comparable to those reported in normal newborn infants. The insulin response to glucose was variable. There were no significant differences with increasing age or between the two groups of infants. The insulin curve of the individual infant followed one of three patterns. Most commonly seen was a double-peak curve. The infants who showed a single-peak insulin response had a better but not significantly different glucose tolerance than that of the other babies. Infants with no appreciable insulin response still removed glucose from plasma at a rate similar to those with a double-peak insulin curve. It is concluded that insulin as measured in peripheral plasma could not explain the rate of removal of glucose from the plasma of the newborn low birthweight infant. Infants of low birthweight had higher plasma FFA values as compared to that reported in normal full term infants. The FFA values in SGA infants were higher than those in AGA babies. In both groups of infants, the jS-hydroxybutyrate values were comparable to those reported in normal full-term babies. Thus there was an unexpected discrepancy between the high FFA and relatively low β-hydroxybutyrate levels in plasma. The fall in plasma FFA and β-hydroxybutyrate after glucose was minimal but similar in both groups of infants. The findings are compatible with a decreased sensitivity to insulin in the infants studied.     

The Normal Development of the Lymphoid Mass in the Golden Hamster and its Relationship to the Effects of Thymectomy

A study of lymphoid organ sections and imprints of normal hamsters fromfetal to adult state revealed a sequential pattern of organ structure and growth.The thymus developed an adult structure by 1 week, maximum size at 6 weeks.The mesenteric lymph node had an adult structure by 4 weeks, the spleen by 6weeks, with an accelerated growth of both organs between 6 to 8 weeks. Thegrowth and development of the peripheral lymphoid organs appears to beunder thymic control until the attainment of a "critical peripheral lymphoidmass." This appears capable of functioning independently of thymic control.Thymectomy is effective in producing lymphoid atrophy with resultant immunosuppression and wasting disease only if performed prior to the attainmentof the "critical peripheral lymphoid mass."

Submitted on February 6, 1964 Accepted on July 26, 1964     

Late Potential Parameter and Noise Level Variability Caused by Bandpass Versus High-Pass Filtering and Type of Signal Averaging Equipment Used

Late potentials detected by signal averaged electrocardiography are predictive of ventricular arrhythmia induction and sudden cardiac death. Prior studies have used a variety of equipment and filtering parameters. The correlation between data from two commercially available signal averaging units and the effects of bandpass as opposed to high-pass filtering were studied in 18 hospitalized patients. The addition of a low-pass filter at 250 Hz to high-pass filtering at 40 Hz caused no significant change in any time domain variable (total duration of the filtered QRS, root mean square voltage of the last 40 msec of the filtered QRS, and duration of low-amplitude potentials < 40 μV). However, the data was significantly different (P < 0.01) when studies from the two machines were compared. We conclude that bandpass filtering does not affect time domain late potential variables in a clinically relevant fashion compared to high-pass filtering alone. Significant data differences exist between the two different pieces of equipment. Therefore, caution should be exercised in extrapolating data obtained from each of the different machines.     

Effects of epidural block with lignocaine and lignocaine-adrenaline on umbilical artery velocity wave ratios

Summary. Umbilical artery blood velocity A/B ratios were recorded in term fetuses once before and twice after the maternal epidural injection of either 8 ml of lignocaine plain (15 women) or lignocaine with adrenaline 1:200000 (40 μg) (16 women). The administration of lignocaine plain led to decreases in the ratio of varying degrees in all fetuses regardless of the height of the initial A/B ratio. The injection of lignocaine with adrenaline produced identical results in fetuses with initially normal A/B ratios. In contrast, all six fetuses with initially high A/B ratios (above 2^.90) who received the adrenaline-containing anaesthetic reacted with a rise in the ratio, and two of these developed transient heart rate decelerations. Thus, if the initial resistance in umbilical blood flow is high, even the small epidural dose of 40 μg of adrenaline produces a further increase which may be associated with clinical implications.     

Circadian Aqueous Flow Mediated by β-arrestin Induced Homologous Desensitization

It was hypothesized that homologous desensitization regulates signal transduction from the beta-adrenergic receptor in the ocular ciliary epithelium to affect the circadian rhythm of aqueous humor secretion. β-arrestin-1 was cloned from the rabbit ciliary epithelium, and the full length cDNA used as a probe for Northern blot analysis to examine the diurnal expression of β-arrestin mRNA. Protein expression of β-arrestin-1 at intervals during the circadian cycle of aqueous secretion showed a decrease in β-arrestin expression when maximal activation of the β-adrenergic receptor is known to increase secretion. Diurnal expression of β-arrestin suggests that homologous desensitization can regulate the circadian rhythm of aqueous flow.